Cellulose type materials are known for use in food products, cellulose powder, microcrystalline cellulose, microfibrillated cellulose (MFC), microbial cellulose (bacteria cellulose, microreticulated cellulose), etc.
Cellulose powder has a large particle size. Accordingly, when blended into a food product that has a low solids concentration, such as drinks, or a food product with a soft mouth-feel, cellulose powder often gives a rough feel upon eating. Thus, its use is limited to shredded cheese (for the prevention of coagulation), cookies (for the improvement of shape retention upon baking), etc.
With respect to microcrystalline cellulose, a new grade of microcrystalline cellulose that disintegrates into small particles in water has been developed. It hardly gives a rough feeling and particularly serves to provide, among others, suspension stability for liquid food products. However, it is characterized by relatively low viscosity, so that it has to be used in a great amount when used as a thickener.
As microfibrillated cellulose, those disclosed in JP-A-56-100801, JP-A-61-215601, JP-A-60-186548, JP-A-9-59302, etc. are known. These are fundamentally produced by passing a suspension of cellulose material through an orifice with a small diameter a number of times while applying a pressure difference of 3,000-8,000 psi (about 21 to about 56 MPa) or 100 kg/cm2 (about 10 MPa) or more. However, under such a pressure difference, microfibrillation cannot progress sufficiently even if the treatment is repeated many times, a large amount of material remains. Accordingly, the mouth feel is adversely affected by the rough and grating feeling. Further, since the absolute quantity of the microfibrillated component is small, it cannot give sufficient viscosity and stability to a food product in many cases.
As a further improvement of the above-mentioned technique, super-microfibrillated cellulose can be referred to, as in JP-A-8-284090. First of all, in this technique, pulp is used as a starting material and it does not matter whatever the species of the original tree is and whatever the method of pulp making is. The starting pulp is preliminarily beaten with a beating machine (beater, Jordin, conical refiner, single disk refiner, double disk refiner, etc.). When the number-average fiber length as measured by the fiber length distribution measurement device (FS-200) manufactured by KAJAANI Co. is 0.8 mm or more, the preliminary beating is carried out until the freeness reaches 400 ml CSF or less. When the number-average fiber length is less than 0.8 mm, the preliminary beating is carried out until freeness reaches 600 ml CFS or less. Then, using an abrasive grain plate type grinding apparatus equipped with an abrasive grain plate composed of abrasive grains having a grain size of No. 16-120 (“Super-grindell” manufactured by Masukou Sangyo K. K.), the freeness is reduced to 300 ml CSF or less. Further, by processing it with a high pressure homogenizer (“Nanomizer” manufactured by Nanomizer Co., Ltd.; “Microfluidizer” manufactured by Microfluidics Co., Ltd.; etc.) at a pressure of 500-2,000 kg/cm2 (about 49-196 MPa), a “super microfibrillated cellulose” having a water retention of 350% or more as determined according to the method indicated in JAPAN TAPPI No. 26, and a number-average fiber length of 0.05-0.1 mm, wherein 95% or more of the integrated fiber number based on the total fiber number has a number-average fiber length of 0.25 mm or less, and the axial ratio of the fiber is 50 or more, can be prepared. According to the JP-A-8-284090 reference, the cellulose particle has “a fiber width of 1 μm or less and the shortest fiber has a fiber length of about 50 μm” as measured by a direct observation using an optical microscope and an electron microscope and, thus, “the axial ratio is 50 or more”.
Although this super-microfibrillated cellulose is suitable for use as an additive to be blended into a coating material for the manufacture of coated paper or a dye or pigment carrier for the manufacture of dyed paper, it contains too large an amount of thick and long fiber component to be used as a material for food products. On the other hand, since the content of fine components that is stably suspensible in water is too low, it fails to give a sufficient stabilizing effect on food products, and, further, gives an unpleasant mouth feel such as roughness to food products. Regarding the fineness of fiber and water-suspension stability brought about thereby, the applicability of the fiber as a material for food products is limited, unless the fineness reaches such a degree that the openings of sieves are clogged making the measurement impossible. Alternatively, all the components pass through the sieve making impossible to obtain any value in the filtration for the water retention measurement as prescribed in JAPAN TAPPI No. 26.
There has also been disclosed a microfibrillated cellulose prepared from beet pulp (JP-A-11-501684). Although this substance is called “cellulose”, it is actually an associated substance of cellulose and pectin or hemicellulose present in beet pulp, which is a main cause of its characteristics, such as high viscosity. Although the pectin and the hemicellulose are defined by “electric charging due to carboxylic acid”, their actual chemical compositions are unknown.
In JP-A-2000-503704, a composition is disclosed wherein cellulose nanofibril is obtained from cells comprising about 80% or more of primary wall and the other additives (30% by weight or less). Although this “cellulose nanofibril” is regarded as substantially the same technique as in JP-A-11-501684, the only difference is that the use of pure cellulose is disclosed. In the JP-A-11-501684 reference, the meaning of using “cells comprising primary wall” as a raw material seems to lie in the degree of crystallinity. In other words, cellulose microfibril derived from secondary wall (for example, wood) has a high crystallinity (higher than 70%) and therefore cannot be made thinner than several tens of nm to several μm. On the other hand, the main object of JP-A-11-501684 is “supplement addition to food products and the like for the purpose of providing some functions of substantially non-crystalline (crystallinity 50% or less) cellulose nanofibril”. Accordingly, the “cellulose nanofibril obtained from cells comprising primary walls of about 80% or more” can be substantially interpreted as “that having a crystallinity of 50% or less”.
Microbial cellulose is also referred to by other names such as bacterial cellulose, bacterial microreticulated cellulose, and fermentation cellulose. Microbial celluloses are produced by the micro-organisms belonging to Genus Acetobacter, Genus Gluconobacter, Genus Pseudomonas, Genus Agrobacterium, etc. This cellulose has a very high purity, and is released out of the microbial cells in the form of well-grown microfibril. For this reason, it is easy to purify and, as a result, the product has a high crystallinity and is useful as a material for crystalline structural analysis of cellulose. Since the cellulose has a unique microfibril structure different from that of other plant cell wall-derived celluloses, its application for an acoustical material, a paper-making additive, and a food additive have been studied. In the application for food products, a thickening function or a suspension-stabilizing function have been recognized. There have been attempts to add a specific polymeric substance to a medium for culturing a micro-organism, or to culture the mixture while agitating it, or to dissociate the product thus obtained, or to use the product as a re-dispersible dry powder (JP-A-3-157402, JP-A-8-291201, and JP-A-2000-512850). However, the production of cellulose by the culture of micro-organism has not yet been established as an economical production technique, since the problems of high cost, low production speed of cellulose, etc., remain unsolved.
It is an object of the present invention to provide a cellulosic material capable of providing a sufficient thickening effect and stabilizing effect (namely, heat resistance, suspension stability and emulsion stability) to food products without adversely affecting the mouth feel thereof by an economical process. Further, it is another object of the present invention to provide a novel gel composition composed mainly of cellulose.